The tissues of the human oral cavity are frequently exposed to repeated low doses of known and suspected carcinogens such as alcohol, tobacco smoke, and x-radiation from diagnostic medical and dental radiology. Previous studies in our laboratory have demonstrated synergy between concurrent topial applications of 7, 12-dimethylbenz(a) anthracene (DMBA) and exposures to modest levels of x-radiation in hamster cheek pouch tumorigenesis. This synergy was manifested by greater tumor incidence, shorter latent period, and greater tumor volume in animals receiving combined treatments than in animals receiving either treatment alone. Radiation enhancement of DMBA lingual tumorigenesis was also observed in similar studies. We have also shown that low-level x-irradiation causes a significant, late increase in cheek pouch vascular volume and that there is a significant interaction between the effects of x-radiation and DMBA or DMBA-induced tumors on cheek pouch functional vasculature. The proposed studies would examine the effects of decreasing radiation dose on DMBA-induced tumor incidence and progression as well as the possible mechanistic role of radiation-induced hemodynamic changes in the induction and progression of these tumors. Young adult male Syrian golden hamsters will receive various doses of DMBA to the cheek pouch accompanied by repeated exposures of 1-20R x-radiation at weekly intervals. The temporal relationships between applications of chemical and radiation will vary. Animals will be observed for varying lengths of time; tumor latency, volume, pathological, and radioisotopic distribution techniques. It is anticipated that the results of these studies will clarify dose-response relationships and time-dose relationships of low level x-radiation in this system, leading to a more quantitative base for calculations of human radiation risk estimates. Additionally, the data should provide information on the nature of radiation induced hemodynamic changes in the induction of epithelial neoplasms by low level exposures to multiple environmental carcinogens.